The reason for a 146-year old Japanese conglomerate like Toshiba is rather simple, as they said in the statement
>"The decision allows each business to significantly increase its focus and facilitate more agile decision-making and leaner cost structures."
Japanese conglomerate has some of the worst bureaucracy in modern cooperate world. Shaped by Japanese history and culture. And in fighting is on a completely different level compared to US or even companies in EUR. Things mostly work if you are not in a technology industry, where things moves relatively slowly. Their CE segment is nearly gone apart from Japanese Market. Their CE outside Japan were sold to Chinese Companies. Their LSI business is out, Their NAND business, despite having higher voting shares, are now partly given control to its partner for better operating efficiency.
It is sad many of these Japanese companies end up like this. Sharp couldn't compete in both LCD and OLED. Japan Display which is the merger of Sony, Toshiba and Hitachi, is barely surviving.
Likely purely because they want to limit corporate liability in case any one of the split companies opens themselves up to massive legal cases/liability.
Also, going into Energy/Infrastructure businesses means (I would hope) more stringent security requirements from government/officials wanting to ensure the safety and security of critical infrastructure - not something a device and storage company really needs to worry about.
For example in 2015 Hewlett-Packard Company split into HP Inc. and Hewlett Packard Enterprise. HP Inc. focuses on personal computer and printer businesses and Hewlett Packard Enterprise focuses on enterprise SaaS.